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MOLECULAR BASIS OF INHERITENCE 1-Transforming principle/
Griffith effect (1928)
This experiment is conducted by Frederick
Introduction Griffith in 1928.
There are 2 types of nucleic acids He conducted experiment on Streptococcus
DNA (Dexoy ribonucleic acid ) pneumoniae (Pneumococcus-It is a coccus
RNA (Ribo nucleic acid ) bacteria that cause pneumonia ).
DNA is the genetic material in most of the During the course of his experiment, a living
organism including human being organism (bacteria) had changed in physical
But there are some viruses (Retrovirus) in form.
which genetic material are RNA. There are 2 strains of pneumococcus bacteria
Examples
S-Strain
HIV,
R-Strain
TMV,
QB Bacteriophage,
Corona Virus
DNA is acidic substance present in the nucleus
was first identified by Friedrich Meischer
(1869). He called it as Nuclein.
Due to technical limitation he could not isolate
such a long polymer S- strain bacteria:
The Search for the Genetic The bacteria produce smooth and shiny colony
in culture plate. This is because the S strain
Material bacteria has mucous (Polysacharide ) Coat.
The discovery of nuclein by Meischer (1869) This strain of bacteria is virulent and cause
and the proposition for principles of pneumonia
inheritance by Mendel (1865) were almost at R strain :
the same time, but that the DNA acts as a It produce rough colonies when grown on
genetic material took long to be discovered culture plate. The rough appearance is due to
and proven. the lack of mucous coat. This type of bacteria
By 1926, the quest to determine the is non virulent and do not cause pneumonia
mechanism for genetic inheritance had Experiment
reached the molecular level. When Griffith injected S strains (Virulent) into
Previous discoveries by Gregor Mendel, Walter mice, they killed them by causing pneumonia
Sutton, Thomas Hunt Morgan and numerous When mice were injected with R strain (Non
other scientists had narrowed the search to virulent ) there was no effect
the chromosomes located in the nucleus of Then, mice were injected with heat killed S strain.
There was no effect.
most cells. But the question of what molecule
was actually the genetic material, had not
been answered.
Navas cheemadan Molecular basis of inheritance/2021
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He then injected a mixture of Heat killed S strain cells. They discovered that DNA alone from S
and Live R strain bacteria, the mice died due to bacteria caused R bacteria to become
pneumonia, moreover , he recovered living S transformed.
bacteria from died mice They also discovered that protein-digesting
enzymes (proteases) and RNA-digesting
enzymes (RNases) did not affect
transformation, so the transforming substance
was not a protein or RNA.
Digestion with DNase did inhibit
transformation, suggesting that the DNA
caused the transformation.
They concluded that DNA is the hereditary
material, but not all biologists were
convinced.
2-Hershey-Chase experiment (1952)
The unequivocal proof that DNA is the genetic
material came from the experiments of Alfred
Hershey and Martha Chase (1952).
They worked with viruses that infect bacteria
called bacteriophages.
He concluded that the R strain bacteria had
somehow been transformed by the heat- Life cycle of Bacteriophage
killed S strain bacteria. Some ‘transforming The bacteriophage attaches to the bacteria
Bacteriophage introduce its genetic material
principle’, transferred from the heat-killed S into the bacterial cell.
strain, had enabled the R strain to synthesise The bacterial cell treats the viral genetic
a smooth polysaccharide coat and become material as if it was its own and subsequently
manufactures more virus particles.
virulent.
Ie. R strain were converted into S strain
This must be due to the transfer of the genetic
material. However, the biochemical nature of
genetic material was not defined from his
experiments.
Biochemical Characterisation of
Transforming Principle
Prior to the work of Oswald Avery, Colin
MacLeod and Maclyn McCarty (1933-44), the
genetic material was thought to be a protein.
They worked to determine the biochemical Hershey and Chase worked to discover
nature of ‘transforming principle’ in Griffith's whether it was protein or DNA from the viruses
that entered the bacteria
experiment.
They purified biochemicals (proteins, DNA, Experiment
RNA, etc.) from the heat-killed S cells to see Hershey and chase grew some viruses in a
which ones could transform live R cells into S medium containing radioactive phosphorus
Navas cheemadan Molecular basis of inheritance/2021
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(32P). Viruses grown in the presence of Bacteria which was infected with viruses that
radioactive Phosphorus (32P) contain had radioactive DNA were radioactive,
radioactive DNA but not radioactive protein, indicating that DNA was the material that
because DNA contains phosphorus but passed from the virus to the bacteria.
protein does not Bacteria that were infected with viruses that
They also grew some viruses (bacteriophages) had radioactive proteins were not radioactive.
on a medium containing radioactive Sulphur This indicates that proteins did not enter the
(35S). Viruses grown in the presence of bacteria from the viruses. DNA is therefore the
radioactive sulphur (35S) contains radioactive genetic material that is passed from virus to
protein but not radioactive DNA because bacteria
protein contains sulphur but DNA does not. DNA (Deoxy Ribonucleic acid)
These Radioactive phages were allowed to It is an acidic substance present in the nucleus
attach to E. coli bacteria. This step is called It was first identified by Friedrich meischer in
Infection 1869
Then, as the infection proceeded, the viral He named it as Nuclein. However due to
coats were removed from the bacteria by technical limitation in isolating such a long
agitating them in a blender. This process is polymer, the elucidation of structure of DNA
called Blending remains elusive
The virus particles were separated from the In 1953, James Watson and Francis Crick
bacteria by spinning them in a centrifuge. This proposed a very simple but famous Double
process is called centrifugation Helical Structure of DNA. They proposed this
model based on X ray diffraction data
proposed by Maurice Wilkins and Rosalind
Frankiln
One of the hallmarks of their proposition was
base pairing between the two strands of
polynucleotide chains.
The length of DNA is usually defined as the
number of nucleotides (Or Base pairs: a pair of
nucleotides)
Eg: Man = 6.6×109 BP
E.Coli =4.6×106 BP
Lambda phage =48502 BP
Ø X 174 phage =5386 nucleotides
(Single stranded DNA)
Structure of DNA
(Read your notebook)
Navas cheemadan Molecular basis of inheritance/2021
SOHSS-Areekode navas cheemadan
MOLECULAR BASIS OF INHERITENCE 1-Transforming principle/
Griffith effect (1928)
This experiment is conducted by Frederick
Introduction Griffith in 1928.
There are 2 types of nucleic acids He conducted experiment on Streptococcus
DNA (Dexoy ribonucleic acid ) pneumoniae (Pneumococcus-It is a coccus
RNA (Ribo nucleic acid ) bacteria that cause pneumonia ).
DNA is the genetic material in most of the During the course of his experiment, a living
organism including human being organism (bacteria) had changed in physical
But there are some viruses (Retrovirus) in form.
which genetic material are RNA. There are 2 strains of pneumococcus bacteria
Examples
S-Strain
HIV,
R-Strain
TMV,
QB Bacteriophage,
Corona Virus
DNA is acidic substance present in the nucleus
was first identified by Friedrich Meischer
(1869). He called it as Nuclein.
Due to technical limitation he could not isolate
such a long polymer S- strain bacteria:
The Search for the Genetic The bacteria produce smooth and shiny colony
in culture plate. This is because the S strain
Material bacteria has mucous (Polysacharide ) Coat.
The discovery of nuclein by Meischer (1869) This strain of bacteria is virulent and cause
and the proposition for principles of pneumonia
inheritance by Mendel (1865) were almost at R strain :
the same time, but that the DNA acts as a It produce rough colonies when grown on
genetic material took long to be discovered culture plate. The rough appearance is due to
and proven. the lack of mucous coat. This type of bacteria
By 1926, the quest to determine the is non virulent and do not cause pneumonia
mechanism for genetic inheritance had Experiment
reached the molecular level. When Griffith injected S strains (Virulent) into
Previous discoveries by Gregor Mendel, Walter mice, they killed them by causing pneumonia
Sutton, Thomas Hunt Morgan and numerous When mice were injected with R strain (Non
other scientists had narrowed the search to virulent ) there was no effect
the chromosomes located in the nucleus of Then, mice were injected with heat killed S strain.
There was no effect.
most cells. But the question of what molecule
was actually the genetic material, had not
been answered.
Navas cheemadan Molecular basis of inheritance/2021
, Join Telegram Channel: https://t.me/hsslive Downloaded from www.Hsslive.in ®
SOHSS-Areekode navas cheemadan
He then injected a mixture of Heat killed S strain cells. They discovered that DNA alone from S
and Live R strain bacteria, the mice died due to bacteria caused R bacteria to become
pneumonia, moreover , he recovered living S transformed.
bacteria from died mice They also discovered that protein-digesting
enzymes (proteases) and RNA-digesting
enzymes (RNases) did not affect
transformation, so the transforming substance
was not a protein or RNA.
Digestion with DNase did inhibit
transformation, suggesting that the DNA
caused the transformation.
They concluded that DNA is the hereditary
material, but not all biologists were
convinced.
2-Hershey-Chase experiment (1952)
The unequivocal proof that DNA is the genetic
material came from the experiments of Alfred
Hershey and Martha Chase (1952).
They worked with viruses that infect bacteria
called bacteriophages.
He concluded that the R strain bacteria had
somehow been transformed by the heat- Life cycle of Bacteriophage
killed S strain bacteria. Some ‘transforming The bacteriophage attaches to the bacteria
Bacteriophage introduce its genetic material
principle’, transferred from the heat-killed S into the bacterial cell.
strain, had enabled the R strain to synthesise The bacterial cell treats the viral genetic
a smooth polysaccharide coat and become material as if it was its own and subsequently
manufactures more virus particles.
virulent.
Ie. R strain were converted into S strain
This must be due to the transfer of the genetic
material. However, the biochemical nature of
genetic material was not defined from his
experiments.
Biochemical Characterisation of
Transforming Principle
Prior to the work of Oswald Avery, Colin
MacLeod and Maclyn McCarty (1933-44), the
genetic material was thought to be a protein.
They worked to determine the biochemical Hershey and Chase worked to discover
nature of ‘transforming principle’ in Griffith's whether it was protein or DNA from the viruses
that entered the bacteria
experiment.
They purified biochemicals (proteins, DNA, Experiment
RNA, etc.) from the heat-killed S cells to see Hershey and chase grew some viruses in a
which ones could transform live R cells into S medium containing radioactive phosphorus
Navas cheemadan Molecular basis of inheritance/2021
, Join Telegram Channel: https://t.me/hsslive Downloaded from www.Hsslive.in ®
SOHSS-Areekode navas cheemadan
(32P). Viruses grown in the presence of Bacteria which was infected with viruses that
radioactive Phosphorus (32P) contain had radioactive DNA were radioactive,
radioactive DNA but not radioactive protein, indicating that DNA was the material that
because DNA contains phosphorus but passed from the virus to the bacteria.
protein does not Bacteria that were infected with viruses that
They also grew some viruses (bacteriophages) had radioactive proteins were not radioactive.
on a medium containing radioactive Sulphur This indicates that proteins did not enter the
(35S). Viruses grown in the presence of bacteria from the viruses. DNA is therefore the
radioactive sulphur (35S) contains radioactive genetic material that is passed from virus to
protein but not radioactive DNA because bacteria
protein contains sulphur but DNA does not. DNA (Deoxy Ribonucleic acid)
These Radioactive phages were allowed to It is an acidic substance present in the nucleus
attach to E. coli bacteria. This step is called It was first identified by Friedrich meischer in
Infection 1869
Then, as the infection proceeded, the viral He named it as Nuclein. However due to
coats were removed from the bacteria by technical limitation in isolating such a long
agitating them in a blender. This process is polymer, the elucidation of structure of DNA
called Blending remains elusive
The virus particles were separated from the In 1953, James Watson and Francis Crick
bacteria by spinning them in a centrifuge. This proposed a very simple but famous Double
process is called centrifugation Helical Structure of DNA. They proposed this
model based on X ray diffraction data
proposed by Maurice Wilkins and Rosalind
Frankiln
One of the hallmarks of their proposition was
base pairing between the two strands of
polynucleotide chains.
The length of DNA is usually defined as the
number of nucleotides (Or Base pairs: a pair of
nucleotides)
Eg: Man = 6.6×109 BP
E.Coli =4.6×106 BP
Lambda phage =48502 BP
Ø X 174 phage =5386 nucleotides
(Single stranded DNA)
Structure of DNA
(Read your notebook)
Navas cheemadan Molecular basis of inheritance/2021
